1. Field
Embodiments of the invention relate generally to a nonvolatile semiconductor memory device and a method for manufacturing the same.
2. Description of the Related Art
Collectively patterned three dimensionally stacked memory is presented in order to increase the memory capacity of a nonvolatile semiconductor memory device (memory) (for example, refer to JP-A 2007-266143 (Kokai]). According to such methods, it is possible to suppress cost increases because a stacked memory can be collectively formed regardless of the number of stacks.
In such a collectively patterned three dimensionally stacked memory, a semiconductor pillar that pierces a stacked structural unit in the stacking direction is provided. The stacked structural unit is formed by alternately stacking insulating films with electrode films that form word lines. A charge storage layer (a memory layer) is provided between the semiconductor pillar and the electrode film. Thereby, a memory cell is formed at the intersection of each electrode film and the semiconductor pillar, and a memory string is formed along the semiconductor pillar.
In order to select the semiconductor pillar that forms the memory string, a selection gate electrode is provided parallel to the electrode film, and a selection gate transistor is formed by the selection gate electrode and the semiconductor pillar. Reducing the resistance of the selection gate electrode is desirable in order to improve the response characteristics of the selection gate transistor.